SIP issues with S/MIME and CMS

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SIP issues with S/MIME and CMS

• Rohan Mahy
• SIP, SIPPING co-chair

2
Very Brief description of SIP

• Rendezvous protocol
• can go direct or use proxies/intermediaries
• register Contacts to an Address of Record
• discover appropriate Contacts
• setup sessions by exchanging offers and answers
• SIP-specific subscribes and notifies
• text-based (looks sorta like HTTP email)
• INVITE siprohan_at_cisco.com SIP/2.0
• SIP/2.0 200 OK / 404 Not Found / etc...
• carries direct or indirect MIME content

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State of SIP security
SIP signaling
media (ex RTP audio, game, chat)

• Digest used for user authentication end-to-end or
  end-to-middle
• TLS used for hop-by-hop server authentication,
  encryption, integrity, and optional mutual
  auth(TLS with RSA, AES128_CBC, SHA1)
• optional IPsec for hop-by-hop encryption and
  integrity
• S/MIME for end-to-end encryption and integrity

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Good reasons for Object security in SIP

• Verifying you are still talking to the same
  person you started talking with (even if they are
  otherwise anonymous)
• SIP for Instant Messaging
• SIP between telephone network devices
• 3rd-party identity assertions for folks you
  authenticated some other way (possibly on a per
  call basis)

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History SIP uses S/MIME

• Mar 1999 RFC-2543 (SIP) published as PS. specs
  PGP for end-to-end security. about 3 early
  implementations, none worked together (badly
  underspecified, lots of implicit behavior)
• Nov 2001 Numerous requests for Digest
  enhancements (including some body integrity stuff
  (see draft-undery-sip-auth-01.txt)
• Dec 2001 PGP Deprecated by SIP WG
• Jan 2002 IESG requests addition of S/MIME to SIP
  spec
• Feb/Jun 2002 RFC-3261 specs S/MIME for
  end-to-end security, provides much more
  motivational text, (ex optional usage with
  self-signed certs), still underspecified
• Mar 2002 draft-peterson-sip-identity-00.txt
  adopted as WG item. Uses S/MIME for 3rd party
  assertion of identity.
• Oct 2002 draft-peterson-sip-smime-aes-00.txt
  proposes update/tighter spec of SIP S/MIME. Uses
  AES.
• Nov 2002 draft-mahy-sipping-smime-vs-digest-00.tx
  t discusses shared-key signing issues.

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What does SIP communitywant from S/MIME?

• Advice from the horses mouth
• Help with S/MIME/CMS implementations -)
• not SIP communitys core competence to add stuff
  to S/MIME or CMS libraries
• Unification of end-to-end/end-to-middle
  authentication, or not (we use Digest and
  S/MIME now)
• SIMPLE needs sessions of messages. should we use
  S/MIME for this? might need shared key
  authentication for this.
• Lots of stuff we want to do with 3rd party
  assertions use signed assertion documents, or
  attribute certs, something else?

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References

• RFC 3261
• draft-ietf-sip-identity-00.txt
• draft-ietf-sip-authid-body-00.txt
• draft-mahy-sipping-smime-vs-digest-00.txt
• draft-peterson-sip-smime-aes-00.txt
• draft-ietf-sip-referredby-00.txt
• draft-ietf-sip-privacy-general-01.txt
• draft-undery-sip-auth-01.txt
• http//www.softarmor.com/sipwg/
• http//www.softarmor.com/sipping/